Vehicle occupant restraint systems which comprise a seat belt are often provided even in compact cars with a belt tensioner which tensions the seat belt in a restraint situation so that the belt is in snug contact with the body of the vehicle occupant. Belt tensioners hitherto conventional are available as retractor tensioners, buckle tensioners or end fitting tensioners secured to differing locations in the vehicle and introducing the force exerted by them correspondingly into differing locations in the belt system.